The present invention relates in general to substrate manufacturing technologies and in particular to an apparatus for an optimized plasma chamber top piece.
In the processing of a substrate, e.g., a semiconductor substrate or a glass panel such as one used in flat panel display manufacturing, plasma is often employed. As part of the processing of a substrate for example, the substrate is divided into a plurality of dies, or rectangular areas, each of which will become an integrated circuit. The substrate is then processed in a series of steps in which materials are selectively removed (etching) and deposited (deposition) in order to form electrical components thereon.
In an exemplary plasma process, a substrate is coated with a thin film of hardened emulsion (i.e., such as a photoresist mask) prior to etching. Areas of the hardened emulsion are then selectively removed, causing components of the underlying layer to become exposed. The substrate is then placed in a plasma processing chamber on a substrate support structure comprising a mono-polar or bi-polar electrode, called a chuck or pedestal. Appropriate etchant source are then flowed into the chamber and struck to form a plasma to etch exposed areas of the substrate.
Referring now to FIG. 1, a simplified diagram of inductively coupled plasma processing system components is shown. Generally, the plasma chamber (chamber) 102 is comprised of a bottom piece 150, a top piece 144, and a top piece cover 152. An appropriate set of gases is flowed into chamber 102 from gas distribution system 122. These plasma processing gases may be subsequently ionized to form a plasma 110, in order to process (e.g., etch or deposition) exposed areas of substrate 114, such as a semiconductor substrate or a glass pane, positioned with edge ring 115 on an electrostatic chuck (chuck) 116. Gas distribution system 122 is commonly comprised of compressed gas cylinders 124a-f containing plasma processing gases (e.g., C4F8, C4F6, CHF3, CH2F3, CF4, HBr, CH3F, C2F4, N2, O2, Ar, Xe, He, H2, NH3, SF6, BCl3, Cl2, WF6, etc.).
Induction coil 131 is separated from the plasma by a dielectric window 104, and generally induces a time-varying electric current in the plasma processing gases to create plasma 110. The window both protects induction coil from plasma 110, and allows the generated RF field 142 to generate an inductive current 111 within the plasma processing chamber. Further coupled to induction coil 131 is matching network 132 that may be further coupled to RF generator 134. Matching network 132 attempts to match the impedance of RF generator 134, which typically operates at about 13.56 MHz and about 50 ohms, to that of the plasma 110. Additionally, a second RF energy source 138 may also be coupled through matching network 136 to the substrate 114 in order to create a bias with the plasma, and direct the plasma away from structures within the plasma processing system and toward the substrate.
Generally, some type of cooling system 140 is coupled to chuck 116 in order to achieve thermal equilibrium once the plasma is ignited. The cooling system itself is usually comprised of a chiller that pumps a coolant through cavities in within the chuck, and helium gas pumped between the chuck and the substrate. In addition to removing the generated heat, the helium gas also allows the cooling system to rapidly control heat dissipation. That is, increasing helium pressure subsequently also increases the heat transfer rate. Most plasma processing systems are also controlled by sophisticated computers comprising operating software programs. In a typical operating environment, manufacturing process parameters (e.g., voltage, gas flow mix, gas flow rate, pressure, etc.) are generally configured for a particular plasma processing system and a specific recipe.
In addition, a heating and cooling plate 146 may operate to control the temperature of the top piece 144 of the plasma processing apparatus 102 such that the inner surface of the top piece 144, which is exposed to the plasma during operation, is maintained at a controlled temperature. The heating and cooling plate 146 is formed by several different layers of material to provide both heating and cooling operations.
The top piece itself is commonly constructed from plasma resistant materials that either will ground or are transparent to the generated RF field within the plasma processing system (e.g., aluminum, ceramic, etc.). Most top piece designs, however, are optimized for operational performance within the chamber itself, and not for other considerations such as ergonomic safety or general thermal performance.
For example, the existing upper portion of the 2300 plasma etch chamber is a monolithic piece of aluminum weighing about 75 lbs, making it substantially difficult to handle during removal, installation, and cleaning. It generally requires at least two workers using some type of lifting apparatus (i.e., winch, etc.) to safely remove the top piece from the plasma processing system.
Historically, since the relative manufacturing cost of the top piece was just a relatively small portion of the overall system cost, there has been no incentive to re-design with smaller amount of material, hence lighter. However, there is growing concern over worker safety, as well as the reduction of worker injuries and subsequently of worker compensation claims. That is, as plasma processing systems have become more sophisticated, many substrate manufactures are able to use fewer less skilled workers in order to save costs, increasing the likelihood of accidental injury.
In particular, ergonomic hazards should be designed out or otherwise reduced to the maximum extent practicable. Ergonomic hazards exist whenever the system design or installation results in task demands (e.g., manipulation of the top piece) that exceed the information processing and/or physical capabilities of trained personnel. In particular, equipment should be designed to fit the physical characteristics of 90% of the user population (e.g. from 5th percentile female through 95th percentile male in the country or region of use.)
Preventive maintenance is also an issue, since the relative heavy weight of the top piece makes the top piece difficult to manipulate, and hence problematic to effectively clean during scheduled maintenance. Cleaning is further aggravated by the presence of plastic and stainless materials on the top piece that limit the types of available cleaning techniques. That is, although a particular cleaning chemical may effectively clean the residue from the top piece, the same chemical may also substantially damage the plastic materials or stainless steel.
In addition, correctly reseating the top piece after maintenance is often difficult, since it must properly be aligned with the bottom piece such that a set of gaskets properly seal around the top piece. A slight misalignment will preclude a proper mating, requiring the workers to try to nudge the heavy top piece into place.
The volume of material in the top piece also tends to add a substantial thermal mass to the plasma processing system. Thermal mass refers to materials have the capacity to store thermal energy for extended periods. In general, plasma processes tend to very sensitive to temperature variation. For example, a temperature variation outside the established process window can directly affect the etch rate or the deposition rate of polymeric films, such as poly-floro-carbon, on the substrate surface. Temperature repeatability between substrates is often important, since many plasma processing recipes may also require temperature variation to be on the order of a few tenths of degree C. Because of this, the top piece is often heated or cooled in order to substantially maintain the plasma process within established parameters.
As the plasma is ignited, the substrate absorbs thermal energy, which is subsequently measured and then removed through the cooling system. However, since the top piece has a relatively large thermal mass, temperature corrections by the cooling system may not be synchronized with temperature variations in the top piece. Subsequently, heat flow variations may cause the substrate temperature to vary outside narrow recipe parameters.
In addition, the location of the heating and cooling plate 146, as shown in FIG. 1, may interfere with electromagnetic field 142. As a high frequency power is applied from the RF power generator 134 to the coil 131, an electromagnetic field is generated, which subsequently generates an inductive current 111 that creates and maintains the plasma. Although not necessarily uniform, the heating and cooling plate 146 may interfere with the electromagnetic field and subsequently affect the uniformity of plasma 110. That is, the resulting electric field may become radial distorted which may result in a substantially non-uniform plasma density across the substrate, potentially affecting yield.
This condition becomes even more problematic as requirements for high circuit density on substrates continue to escalate. For example, in a plasma etch process, if the plasma is not properly optimized, faceting may occur. A facet is a non-linear profile of a feature on the substrate, such as with a trench sidewall. A region of low plasma density may not remove a sufficient amount of material from the substrate, subsequently reducing the size of a trench or via. Likewise, a region of high plasma density may remove an excess amount of material from the substrate subsequently creating a cavernous undercut.
In view of the foregoing, there are desired methods and apparatus for optimizing a process model in a plasma processing system.